In recent years, LED modules have been employed as light sources for illumination apparatuses.
FIG. 75 shows one example of a conventional LED module. As shown in FIG. 75, an LED module 900a includes a rectangular substrate 910 made of glass epoxy resin, and three LED chips 931, 932 and 933 mounted on the substrate 910. A plurality of electrodes 921, 922, 923 and 924 is formed on the substrate 910. The LED chips 931, 932 and 933 are die-bonded to the electrodes 921, 922 and 923, respectively. The electrode 924 is a so-called common electrode and makes conductive connection with the LED chips 931, 932 and 933 via wires 940. The three LED chips 931, 932 and 933 are surrounded by a case 950. The case 950 is a frame-like opaque resin material and has its inner space filled with transparent resin (not shown). The LED module 900a is configured as a side view type LED module that is mounted on a circuit board or the like, with a lower surface extending in the longitudinal direction of the substrate 910 as a mounting surface. The LED chips 931, 932 and 933 emit red, green and blue light, respectively. The LED module 900a aims to emit white light by mixing the lights emitted from the LED chips 931, 932 and 933.
The LED module 900 is required to emit light with high luminance because it may be used as an illumination light source for a variety of electronic devices. However, the LED chips 931, 932 and 933 generate heat due to their emission. If this heat increases the temperature of the substrate 910 excessively, the substrate 910 made of glass epoxy resin is likely to be unduly deformed.
Recently, it has been increasingly required that an LED module emit light close to natural light for illumination of a room. This recent trend results in LED modules configured to emit white light.
FIG. 76 shows one example of a conventional LED module configured to emit white light. As shown in FIG. 76, an LED module 900b includes a substrate 91 made of glass epoxy resin, and an LED chip 92 mounted on the substrate 91. A case 93 is attached to the substrate 91. The case 93 has an opening 935 formed to expose the LED chip 92. The LED module 900b further includes a fluorescent resin 94 with which the opening 935 is filled. In addition, a lens member 95 to cover the fluorescent resin 94 is attached to the case 93.
The LED chip 92 is configured to emit, for example, blue light. The fluorescent resin 94 emits yellow light by absorbing blue light emitted from the LED chip 92. The LED module 900b emits white light by mixing the blue light and the yellow light.
The color temperature of the white light emitted from the LED module 900b is determined by the LED chip 92 and the fluorescent resin 94. The color temperature is an index indicating a relative strength between the blue-violet light and red light in the white light. A higher color temperature provides more blue-violet light, whereas a lower color temperature provides more red light. The color temperature of the white light may be varied by changing the ingredients of the fluorescent resin 94. There is a need to provide the fluorescent resin 94 that is able to obtain light having a color temperature according to a consumer's taste.
Further, there is a need for mass production of the fluorescent resin 94 in order to reduce the production costs of the LED module 900b. Therefore, the manufacturability of the fluorescent resin 94 is limited by material price and the amount of material available. Accordingly, it is not necessarily the case that a fluorescent resin capable of obtaining light having a color temperature according to a consumer's taste can be easily produced.
FIG. 77 shows another example of a conventional LED module. As shown in FIG. 77, an LED module 900c includes a substrate 901 and an LED chip 902 mounted on the substrate 901. A frame-like reflector 905 is formed on the substrate 901. The reflector 905 has a reflecting surface 906 surrounding the LED chip 902. The space surrounded by the reflecting surface 906 is filled with a sealing resin 907. The LED chip 902 includes a submount substrate 903 made of Si and a semiconductor layer 904 stacked on the submount substrate 903. The semiconductor layer 904 makes conductive connection with the substrate 901 via the submount substrate 903.
There is a strong need for compactness of the LED module 900c. To facilitate reduction of the size of the LED module 900c, the angle of the reflecting surface 906 needs to be adjusted to follow the vertical direction in FIG. 77. As the reflecting surface 906 is adjusted to be aligned with the vertical direction, light emitted from the LED chip 902 toward the reflecting surface 906 propagates in the sealing resin 907 at an angle closer to the horizontal direction after being reflected by the reflecting surface 906. This light is likely to be completely reflected on the top side of the sealing resin 907.
LED modules containing LED chips that are capable of emitting white light are widely used for light sources of a variety of electronics. An LED module capable of emitting white light includes, for example, an LED chip which emits blue light and a fluorescent portion which covers the LED chip. The fluorescent portion is obtained by mixing fluorescent material in transparent resin. Examples of the fluorescent material may include red fluorescent material which emits red light when it is excited by blue light, green fluorescent material which emits green light when it is excited by blue light, and a combination thereof. When the blue light, the red light and the green light are mixed together, white light is emitted from the LED module.
Depending on the application of an LED module, it may be important to reproduce the inherent tone of an illuminated object. This color rendering property is commonly estimated by using an average color rendering index (hereinafter, referred to as “Ra value”) defined by JIS (Japanese Industrial Standards). A simple mixture of blue light, red light and green light may not necessarily provide a sufficient Ra value. Applications placing stress on the color rendering property require an LED module having an Ra value as large as possible.